The present invention relates to a commutator motor, and more particularly, to a commutator motor which is employed for a power tool or the like and mainly driven by a battery, and is relatively large in size.
As a motor employed for the power tool or the like, a commutator motor is known, and the commutator motor of this type is generally driven by a battery.
Japanese Patent Application Publication No. Hei-11-136883 discloses a commutator motor which is relatively small in size. The commutator motor includes a housing, a stator, an armature, a brush and a commutator, and the stator includes a cylindrical stator yoke which is substantially rectangular columnar in contour and a field magnet. The inner peripheral surface of the stator yoke is circular in a section vertically taken along an axial direction thereof, while an outer peripheral surface of the stator yoke has a rectangular cross-section. The rectangular outer surface portion has four corners, and a yoke section projecting radially outwardly is provided at each corner. A field magnet is disposed between the neighboring two yoke sections. Therefore, there are four field magnets in total which are fixed to positions that are radially outside of the stator yoke and opposite to each other in the diameter direction of the stator yoke. The stator yoke is structured by stacking steel plates on each other, and the field magnet is formed of a permanent magnet. Four field magnetic poles are generated at the stator by the field magnet, and a magnetic field is developed by the four field magnetic poles.
The brush is fixed to the housing through a brush retaining device. The housing is substantially cylindrical and coaxially connected to the stator yoke in an immovable manner. The brush retaining device is disposed on and protrudes radially inwardly from an inner peripheral surface of the housing, and the brush projects inwardly in the radial direction of the housing by the brush retaining device. The brush is electrically connected to a battery that constitutes a power source.
The armature is disposed inside of the stator and includes a shaft, a core and a coil. The shaft is disposed at the position of the axial center of the stator yoke so as to be rotatable with respect to the stator yoke. The core is fixed to the shaft and has a plurality of slots formed therein. A conductor wire is wound around the core while being hooked by the slots, and the wounded conductor wire forms a coil. Also, the substantially columnar commutator is coaxially fixed to the shaft at a position on the shaft opposing the brush, and the shaft is so structured as to rotate together with the commutator and the core. The commutator is electrically connected to the coil and always comes in contact with the brush. An electrical current is supplied to the coil through the brush and the commutator so that a rotational torque is developed in the armature.
In the conventional commutator motor described above, the stator yoke is structured by stacking the steel plates on each other. However, there is no disclosure of a method for coupling the adjacent steel plates to each other in the stacking direction. For example, it is conceivable that the adjacent steel plates are fixed to each other by caulking. However, because the conventional permanent magnet commutator motor is small in size, there is a fear that the steel plates are deformed when concaves and convexes are formed on the steel plates for caulking, and it is actually impossible to fix the steel plates by caulking. Also, because the field magnet is disposed on the radially outer side of the stator yoke, the magnetic flux cannot be effectively utilized, which lowers performance of the motor.